The background of the invention will be set forth in two parts.
The present invention generally pertains to the field of building construction and building remodeling, and more particularly to the field of roofing for residential buildings.
Over the years the use of man-made materials as replacement for naturally occurring materials, such as wood and slate for example, in order to reduce the cost of roofing have become increasingly popular. In fact, a very large industry has been developed to produce roofing using asphalt-based materials. These products have become very popular because of their ease of use and relatively low cost as compared with the aforementioned wood and slate and as also compared with traditional man-made tile roofing.
With the advent of plastics, much research has gone into adapting its use to the roofing industry. At first, the synthetics were applied in sheet form only for their water-resistant qualities, but more recently attention has been focused on polystyrene and polyurethane foams for their heat and sound insulating characteristics.
Probably the widest use of such lather foam which is formed from a foamable polyurethane resin reaction mixture is to apply it while in a liquid state by hose and spraying equipment directly onto a roof bed. This technique has proven itself to be very valuable for commercial building projects, but because of its cost and the fact that it is only practical on relatively flat roofs, and because it is not very pleasing aesthetically, it is not generally used as a residential roofing medium.
Noting the desirable heat and sound insulating qualities, the industry has worked with the polyfoam in the form of boards or large rectangular sheets having opposite broad flat surfaces from one to two inches in thickness. Invariably, impermeable plastic sheets or layers of felt and bituminous material are cemented or otherwise bonded to the roof support structure prior to laying down the foam boards so that water cannot seep through the seams between abutting ones of these boards. Also, protective layers are generally provided on the outer flat surface of the foam boards in order to lessen decomposition thereof when certain ones of the foam materials are exposed to wind, rain and sunlight.
Not only is this latter technique very complicated and costly, but also the results leave much to be desired as to eye appeal. Accordingly, it has been found that this flat-type construction is not generally desired by home owners and is seldom used.
In order to overcome this disadvantage and in order to eliminate the need for a truss element (since these panels lack strength to support themselves), a newer scheme has developed whereby laminated plastic boards or panels, including a foam core, are bent to a desired curvature. Since a flat board of foamed polyurethane that has been arched or curved has a strong tendency to assume its original flat shape, a structural tie must necessarily be provided between the inner and outer layers of the curved panel material to hold the panel at the desired curvature. This can be accomplished, for example, by piercing the foam with a number of holes at predetermined intervals and filling the holes with a fiber glass resin composition to chemically bond with the same material coated on the surfaces of the foam.